The present invention is directed to a phase-control power controller that supplies a specified power to a load, and more particularly to a voltage converter for a lamp that converts line voltage to a voltage suitable for lamp operation.
Some loads, such as lamps, operate at a voltage lower than a line (or mains) voltage of, for example, 120V or 220V, and for such loads a voltage converter that converts line voltage to a lower operating voltage must be provided. The power supplied to the load may be controlled with a phase-control circuit that typically includes an RC circuit. Moreover, some loads operate most efficiently when the power is constant (or substantially so). However, line voltage variations are magnified by these phase-control circuits due to their inherent properties (as will be explained below) and the phase-control circuit is desirably modified to provide a (nearly) constant RMS load voltage.
When the phase-control power controller is used in a voltage converter of a lamp, the voltage converter may be provided in a fixture to which the lamp is connected or within the lamp itself. U.S. Pat. No. 3,869,631 is an example of the latter, in which a diode is provided in the lamp base for clipping the line voltage to reduce RMS load voltage at the light emitting element. U.S. Pat. No. 6,445,133 is another example of the latter, in which transformer circuits are provided in the lamp base for reducing the load voltage at the light emitting element.
Factors to be considered when designing a voltage converter that is to be located within a lamp include the sizes of the lamp and voltage converter, costs of materials and production, production of a potentially harmful DC load on a source of power for installations of multiple lamps, and the operating temperature of the lamp and an effect of the operating temperature on a structure and operation of the voltage converter.